1. Field of the Invention
The present invention relates to a technology for switching ringlets in a ring network configured with a plurality of ringlets.
2. Description of the Related Art
Conventionally, Resilient Packet Ring (RPR) has been paid attention to as a technology for constructing backbone networks owned by carriers or the like. As for a RPR composed of double ringlets, various functions, such as a function of selecting the ringlet, a function of using a ringlet bandwidth, and a function of switching to another ringlet upon occurrence of failures are specified by Institute of Electrical and Electronic Engineers (IEEE) (IEEE-802.17).
When specifically explaining the RPR, the ringlet of the RPR is configured by interconnecting a plurality of frame transfer apparatuses called “stations” to each other in a ring-type manner as shown in FIG. 25, and has a double ringlet configuration by doubly interconnecting adjacent “stations” to each other. These double ringlets mutually transfer frames in the opposite directions (refer to a ringlet 0 and a ringlet 1 in FIG. 25), wherein when the “station” transfers the frame to the “station” of a transfer destination, one ringlet of the double ringlets is selected for every “station” of the transfer destination as shown in FIG. 26, and the frame is transferred to the adjacent “station” by making use of the selected ringlet. Additionally, when a failure occurs in one ringlet, the “station” selects the other ringlet in which no failure occurs, and switches to the selected ringlet to transfer the frame to the adjacent “station”.
Here, since one ringlet of the double ringlets is necessary to be selected in the RPR as explained above, a technique of selecting the ringlet and a technique of switching to the selected ringlet have been proposed. For example, as the technique of selecting the ringlet, IEEE 802.17 specifies a technique of selecting a ringlet having the fewer number of hops to the “station” of the transfer destination of the frame (the number of “stations” passed through the “station” of the transfer destination). As the technique of selecting and switching to the ringlet upon occurrence of failures, IEEE 802.17 also specifies a technique of selecting and switching to the ringlet so as not to pass through a section where the failure is caused.
Additionally, as the technique of selecting and switching the ringlet, a technique of selecting the other ringlet when the traffic amount of the ringlet having the fewer number of hops is not less than a threshold is disclosed in Japanese Patent No. 2005-354598, for example.